Process for preparing diolefins



, Patented May 22, 1945 PROCESS FOR PREPARING DIOLEFIN S Frederick E. Frey, Bartlesville, kla'., assignor to Phillips Petroleum Company, a, corporation of Delaware Application November 29, 1941, Serial No. 421,067

3 Claims.

This invention relates to the preparation of aliphatic conjugated diolefins and more particularly to their preparation by thermal conversion of hydrocarbon material consisting essentially of a C2 or C3 parafiin or olefin, namely ethane, ethylene, propane, propylene and mixtures of any two or more thereof.

The principal object of the present invention is to prepare by thermal conversion aliphatic conjugated diolefins in higher yield and in higher per pass quantity than in earlier forms of the pyrolytic type of process.

A further object is to recover an aliphatic conjugated diolefin concentrate free from undesired materials and particularly undesired diolefins, from the pyrolytic reaction product inspite of the difficulties presented by the presenc of a great variety of hydrocarbons in the effluent.

A still further object is to prepare a mixture consisting essentially of butadiene with non-cyclic pentadienes which has peculiar value inproducing, upon polymerization, sy thetic rubber having good processing characteristics.

Numerous other objects will more fully hereinafter appear.

In accordance with my invention, I subject to pyrolysis a raw feed consisting essentially of ethane, ethylene, propane, or propylene, or mixtures thereof. As raw material I prefer to use substantially pure ethylene or a C2 material which is predominantly ethylene. I have found that even when a C2 material predominantly or exclusively ethylen is pyrolyzed, the formation of C hydrocarbon is rather marked. Whereas the C4 hydrocarbons contained in the reaction product contain virtually no cyclic material, I have found the C5 hydrocarbons to contain, due to reactions not thoroughly understood, a considerable amount of cyclopentadiene and cyclopentene which lowers the yield of the desired aliphatic conjugated diolefins, especially pentadienes, and renders diflicult the recovery of pure aliphatic conjugated diolefln.

In accordance with my invention, the C2 and/or Ca paraflin or olefin hydrocarbons are pyrolyzed by heat treatment at 'a pressure substantially atmospheric, at a temperature of from about 1450" to about 1600" F. for a period of of from about 2 seconds to about one-tenth of a second- With the pyrolysis thus controlled. there results an emuent containing from about one and one-half to about six weight per cent of butadiene, together with other 04 hydrocarbons, and

per cent of pentadieneacomprislng amixture of isoprene, piperylene and cyolopentadiene. mixture usually contains some cyclopentene.

This efiluent is now fractionated toseparate a fraction comprising all the C4 and C5 hydrocarbons from lower boiling and higher boiling ma- The terial. If desired, either the lower boiling, or the after separation of any non-paraihns and non olefins, is perfectly feasible provided the amount recycled is not so great as to destroy the predominantly C2 to Ca parafiin and/or olefin nature of the feed. If desired or necessary, the lower boiling material may be treatedto remove any material other than C2 and Ca paraflins and olefins before recycling. Acetylene, if returned, contributes to the diclefin yield Removal of nonparaflins and non-olefins other than acetylenes and which may comprise aromatics, and other cyclic hydrocarbons from any material recycled in the process of the present invention is desirable to insure a higher yield of the desired diolefins and to prevent formation of undesirable byproducts.

The C4 and C5 fraction thus recovered is now preferably treated to remove the cyclopentadiene present invention. This may be done in a variety from about one to about two and one-half weight of ways. A preferred way is to subject the fraction in the liquid phase to thermalization in known manner to convert the cyclopentadiene content selectively to the dimer without affecting acetone condensation procedure to remove the cyclopentadiene, a

If desired,-remova1of cyclopentadiene may pre-.

cede fractionation to. recover the terial.

. The C4 and C5 material resulting, thus freed of cyclopentadiene, is admixed with sulfur dioxide C4 and Cs ma and subjected to thermal conversion preferably liquid phase and at a reaction temperature above the ceiling temperature for polysulfone formation, that is to say, under a pressure of from about 500 to about 3000 pounds per square inch and at a temperature of from about 110 to about 300 C., as disclosed in my copending application Serial No. 421,068, filed November 29, 1941 The monosulfones of the aliphatic conjugated C4 and C5 diolefins are formed by the reaction with sulfur dioxide. These are separated from unreacted materials (S02 and non-dioleflnic C4 and C5 hydrocarbons) in any suitable manner. it being preferred to distill oif the unreacted materials from the monosulfones, thus taking advantage of the low volatility of the latter.

The monosulfones are now thermally cracked at low pressure, say about atmospheric, and at a temperature above their decomposition point, namely at least-about 120 C., to regenerate the diolefins which consist of a mixture of butadiene, isoprene and piperylene, the butadiene being predominant. This mixture is particularly suitable of the monosulfones and consisting of sulfur dioxide and the diolefins are quickly cooled to a temperature sufficiently low to prevent re-reaction, and are then treated in such a way as to separate the sulfur dioxide from the diolefins as by fractional distillation or, preferably, by extraction of the diolefins with a comparatively high boiling mineral oil of low compatibility with sulfur dioxide as disclosed in my copending application serial No. 423,535, filed December 18, 1941.

If desired the mixture of butadiene, isoprene, and piperylene thus obtained may be partially or completely resolved into its several components. 01' the mixture of monosulfones may be subjected to successively more drastic thermal treat: ment to successively decompose the several monosulfones in the order of their thermal instability, the decomposition products being separately recovered. For example the separation of the isoprene and 'butadiene from the piperylene may be effected by a successively mild and drastic thermal treatment to decompose their sulfones in the order named, taking advantage of the difference in thermal stability.

The olefinic and paraffinic C4 and C5 hydrocarbons present in the mixture of unreacted products from which the monosulfones were removed, may be separated from unreacted sulfur dioxide and, if necessary, from any other undesirable material which may be present. such a non-paraffins and non-olefins and recycled to the initial cracking operation. The sulfur dioxide may be separated from the associated light hydrocarbons by physical extraction of the mixture with a comparatively high boiling hydrocarbon oil of low compatibility with sudfur dioxide.

I have found it to be particularly desirable, in the separation of sulfur dioxide from unreacted C4 and C5 hydrocarbons to subject the S02. C4

. rate the other C4 and C5 hydrocarbon from the and C5 mixtureto fractional distillation whereby out at the top. The absorbed hydrocarbon is" lene.

removed from the oil by the usual stripping process.

The sulfur dioxide recovered both from the unreacted mixture left upon monosulfone separation and from the decomposition of the monosulfone is preferably recycled.

The accompanying drawing portrays 'a flow diagram of the process outlined above.

With regard to recycling of hydrocarbons other than C4 and C5 diolefins derived from the reaction eiiiuent, and particularly of parafiins and olefins derived from the reaction eflluent, it is preferred to recycle only the C2 and C3 parafiins Example Fairly pure ethylene is pyrolyzed at atmospheric pressure by passingthrough a tube in which it is maintained at 1475 F. for 1 second.

The reaction eilluent contains 4.2% of butadiene and 1.7% of pentadienes of which 0.4% is cyclopentadiene; This eflluent is cooled and fractionated to separate the C4 and C5 material. The C4 and C5 fraction is then treated to remove the cyclopentadiene content by heating to 135 C. for 60 minutes, followed by distillationto separesidue comprising the dimer of cyclopentadiene.

The resulting C4 and C5 fraction is then admixed with sulfur dioxide in amount equal to twice the stoichiometric equivalent of the diolefln content thereof and the mixture heated 'at 700 pounds per square inch pressure and at a temperature of 135 C. for 3 hours. The monosulfone formed is separated from unreacted components and is subjected to heat treatment at C. at atmospheric pressure to form a mixture of sulfur dioxide, butadiene, isoprene and pipery- This mixture is quickly cooled to 30 C. and is subjected to extraction with high-boiling mineral oil to remove the diolefin content. Upon stripping the rich oil, the pure diolefins are re covered and analyze as follows:

' Per cent 68 21 11 It will be seen from the foregoing that the present invention provides an improved method of preparing mixed or single diolefins suitable for polymerization to synthetic rubber from readily available materials at the refinery, in a simple and economical manner.

It is to be understood that the invention is capable of numerous modifications and is not restricted to the foregoing description which is illustrative only of the preferred mode of procedure. For example, the invention may in some cases be modified so that Cs aliphatic-conjugated diolefins are prepared and are recovered along with or separately from the C4 and C5 aliphatic conjugated diolefins. The invention, therefore, is to be taken as limited only by the language of the appended claims.

Butadiene Isoprene Piperylene pentadiene content thereof by thermally dimerizing the cyclopentadiene and distilling the C4 and C5 fraction from the dimer, removing traces of cyclopentadiene by condensation with acetone, reacting the cyclopentadiene-free C4 and C5 fraction with sulfur dioxide to selectively convert substantially all of the diolefins contained therein to the monosulfone, separating the mixture of diolefin monosulfones thereby formed from the unreacted materials, and thermally decomposing said monosulfones to regenerate the butadiene, piperylene and isoprene therefrom.

2. The process of recovering butadiene, piperylene and isoprenefrom the eilluent of the pyrolysis of a hydrocarbon comprising predominately an aliphatic hydrocarbon having from 2 to 3 carbon atoms andat least as saturated as an olefin at substantially atmospheric pressure, at a temperature ranging from about 1450 to about 1600 F. and for a contact time ranging from about 2 to about 0.1 second, which comprises iractionally distilling said eilluent and thereby segregating a single fraction consisting ofv all the C4 and C5 hydrocarbons contained therein, removing the cyclopentadiene content of said fraction by thermalizing said fraction in the liquid phase to selectively convert said cyclopentadiene content to the dimer, distilling the resulting mixture to separate C4 and C5 fraction from said dimer, condensing traces of cyclopentadiene in the resulting distillate with acetone in the presence of an alkali alcoholate, and subjecting the resulting mixture to distillation to separate from the condensation product of said cyclopentadiene and said acetone, removing the aliphatic conjugated dliolefin content of' the resulting cyclopentadiene-free fraction by reacting substantially only said aliphatic conjugated diolefin content of said fraction with sulfur dioxide to form the monosuliones of butadiene, piperylene and isoprene in admixture and separating said mixture of monosulfones from the unreacted materials, and thermally decomposing said monosulfones to regenerate the butadiene, piperylene and isoprene therefrom.

3. The process of claim 1 wherein the last step thereof is conducted by subjecting saidmixture of monosulfones t0 successively more drastic thermal treatment to decompose said monosulfones in the order of their thermal instability, and separately recovering th thus regenerated butadiene, piperylene and isoprene.

FREDERICK E. FREY. 

